1. Field of the Invention
The present invention generally relates to printed circuit boards. More particularly, the present invention relates to a method and apparatus for manufacturing printed circuit boards. Still more particularly, the present invention relates to a new, cost effective manufacturing technique for cutting ("dicing") a circuit board substrate that also permits an increase in the density of components on the board.
2. Background of the Invention
Many types of electronic equipment include printed circuit boards. A printed circuit board ("PCB") generally includes a substantially rigid substrate constructed from ceramic or other suitable material, semiconductors and other types of interconnected electronic components attached to the substrate. PCB's are widely used in a wide variety of electronic equipment such as computers, calculators, telephones, watches, pacemakers and cellular telephones.
Usually it is desirable, and in many instances imperative, that devices, such as laptop computers, implantable medical devices and cellular telephones, be as small as possible. Accordingly, the components used to construct such devices, including the PCB, must be miniaturized as much as possible. It is also desirable to reduce manufacturing cost whenever and wherever possible. Thus, designers and manufacturers of PCB's continuously strive to provide smaller, less expensive circuit boards that lower the cost of the finished product. The present invention generally relates to a method and apparatus for making PCB's smaller and less costly than previously possible. To fully appreciate the benefits of the invention, a conventional technique for manufacturing a typical PCB will now be described.
Referring first to FIG. 1, the layout of a conventional PCB 20 includes a substrate 22 and one or more electronic components 32 mounted on one or two sides of the substrate 22. The components 32 are mounted in a central circuit area 28 of the substrate 22. Usually, in the initial stages of manufacturing, the PCB 20 includes waste edges 24 (also referred to as "wings") on either side of the central circuit area 28. The waste edges 24 result from the fact that the raw substrate 22 typically is manufactured in a predefined width W, but the central circuit area 28 does not require the full width of the substrate 22. Also, one or more conductive test pads 26, electrically connected to various components 32, are included in central circuit area 28 for testing purposes as explained below.
A typical PCB manufacturing process will now be explained. As shown in FIG. 2, the substrate 22 is manufactured in step 40 and prepared for use to assemble the PCB. Step 40 includes creating all of the conductive traces on and within the substrate 22 for interconnecting the components that will be mounted on the substrate in step 50. In step 46 the waste edges 24 are removed using a conventional PCB chuck saw. The saw includes an electrically-controlled chuck table 34 as shown in FIG. 3 which has a substantially flat workpiece fixture 36 on which the PCB is placed. A precision circular saw (not shown) then is used to cut the substrate along lines 30 (FIG. 1) separating waste edges 24 from central circuit area 28. The table fixture 34 uses vacuum suction to hold the PCB 20 in place while the cutting step is performed. The vacuum is supplied from a vacuum pump (not shown) through slots or holes 38 in the workpiece fixture 36. As can be seen in FIG. 3, the workpiece fixture 36 of the chuck table 34 is flat to permit adequate suction for holding the PCB 20 in place. To use this type of chuck table, the PCB 20 must also be flat during cutting step 46, and thus the electrical components to be mounted on the substrate 22 typically are not mounted until after the waste edges are cut off.
Although it is desirable to cut through the substrate 22 in step 46, for obvious reasons it is not desirable to cut the top surface of the workpiece fixture 36 holding the PCB 20 and place. To avoid cutting the workpiece fixture 36, an adhesive polymer tape is applied to the bottom surface of the PCB 20 in step 42. The polymer tape acts as a spacer and typically is 0.003-0.005 inches thick. Further, the substrate 22 and polymer tape are baked in step 44 to activate the adhesive in the tape.
It is important to maintain the PCB 20 as clean as possible and to protect it from damage during manufacturing. To avoid damaging the PCB once the waste edges 24 are removed, the PCB is placed in a protective carrier (carrier not shown) in step 48. The carrier may be constructed from plastic or other suitable type of material and is generally a rigid structure whose purpose is to protect PCB during the remainder of the manufacturing process. In step 50, the components are mounted on the substrate 22 using conventional surface mount technology (SMT) or other suitable manufacturing technology. In step 52 the completed PCB is tested to insure that it functions as intended. The testing process typically includes one or more electrical tests in which the circuit on the PCB 20 is activated and the signals on the test pads 26 are monitored for proper signal level and timing. If the PCB passes testing, it is then assembled into the electrical equipment or sold as a separate component.
Because of the relatively high complexity of the conventional manufacturing method of FIG. 1, the potential for errors to occur is significant. Each step of a manufacturing process has risks for errors to occur. A process with many steps, therefore, has a greater chance for errors to occur than a process with fewer steps. Accordingly, it would be desirable to have a PCB manufacturing process with fewer steps than the conventional process of FIG. 2.
Additionally, the cost involved with the conventional manufacturing process shown in FIG. 2 is substantial. The cost includes:
The carriers used to hold and protect the PCB after the waste edges 24 are removed. PA1 Cleaning and recycling the carriers for use with subsequent PCB's. PA1 The polymer tape applied to the bottom surface of the substrate 22. PA1 The oven needed to activate the polymer tape's adhesive.
These costs and others drive up the price of the finished PCB. It is desirable to minimize manufacturing costs as much as possible.
As noted above, it is also desirable to miniaturize many PCB's to the fullest extent possible. Miniaturization involves two related aspects: (1) implementing a circuit on a PCB so as to take up as little surface area as possible, and (2) manufacturing a PCB to include as many components as possible in a given space. In either case, the "density" of the circuit is increased. The goal of PCB miniaturization generally involves includes the component density.
It would be highly desirable to have a less costly PCB manufacturing process. It would also be desirable to have a PCB manufacturing process for making PCB's with higher component density. Such PCB's would result in lower priced, smaller equipment that incorporate such PCB's.